It is known to provide buoyant off-shore platforms, such as well-drilling platforms, docks and barges, which can be floated to a desired position and then supported from the submerged bottom in an above-water position by means of vertical tubular legs or caissons. A typical platform has four or more legs each carried by a jacking device which is capable of effecting relative vertical movement between the leg and the platform. After the floating platform has arrived at the desired location the jacking devices lower the legs into contact with the submerged bottom. Once the legs become embedded in the bottom and cease to move downwardly continued operation of the jacking devices causes the platform to rise out of the water relative to the legs. Jacking is stopped when the platform reaches an elevation at which it is unaffected by wave action. The platform can be moved to another site by lowering it down into the water, raising the legs away from the submerged bottom and towing or propelling the platform through the water. Platforms of this type are more fully described in a number of United States patents of which U.S. Pat. No. 2,775,869 (Pointer) is exemplary.
The use of such floating jack-up platforms to erect a pier for ship loading and unloading has been suggested in the past. The principal advantage of the technique is that the pier can be erected at a remote site in a much shorter time than would be required if conventional construction methods are used. The savings in erection time result primarily from the facts that the platforms are prefabricated at a shipyard where all construction facilities are available and that essentially the platforms need only be jacked-up once they arrive at the remote site. The technique does include a delay, however, in that the marine transport time is considerable. The usual method of transport is by towing, and the weight, shape and design of the platforms limits the towing speed to substantially less than the speed of, for example, a cargo ship. Currently platforms of this type can be towed successfully about 100 miles per day. Self-propelling the platforms would not significantly improve the speed.
There is therefore a need to provide a system for transporting and erecting a pier facility in a shorter time than is presently available. The shorter time period is of strategic advantage in providing equipment, food and supplies during military and naval operations and is also of advantage in setting up relief operations to supply food and supplies in the event of natural disasters and in erecting piers in polar areas where navigation is restricted to a short period each year. Generally such systems are intended for erecting a temporary facility which can be disassembled and moved to another site or to a storage area.
According to the invention there is provided a method of establishing a ship loading or unloading facility which comprises: providing a buoyant self-propelled vessel capable of substantial speed and having removable jack-up legs adapted to be stored in generally horizontal positions on the vessel and to be inserted vertically in jacking devices carried by the vessel, the vessel having a space carrying a plurality of buoyant jack-up platforms or barges and having a load lifting crane; propelling the vessel to an off-shore location adjacent a shore where it is desired to load or unload a cargo ship; releasing the buoyant platforms from the vessel; jacking-up the vessel to render it stationary; and, jacking-up the platforms in an arrangement between the vessel and the shore to provide access for road vehicles, whereby a cargo ship may be moored to the jacked-up vessel so that cargo may be transported by the crane from the ship to an adjacent barge or in the reverse direction. This method, using a vessel of conventional speed, is capable of moving all of the essential parts of a loading and unloading facility to a site at a speed substantially in excess of that possible by towing. A typical vessel speed of 20 knots is equivalent to about 500 miles per day as compared to a typical towing rate of 100 miles per day.
According to another feature of the invention the jack-up platforms or barges are loaded into and unloaded from the jack-up vessel by floating them into or from a well provided in the vessel. This can be accomplished by having the well open through the stern of the vessel and by providing the vessel with ballast tanks capable of lowering the stern to place the well in communication with the sea. The forward end of the well need not become flooded to a depth equal to the draft of the buoyant platforms. Once the forward end of a platform has entered the opening in the stern of the vessel the platform can be winched forward along rollers provided on the bottom of the well. Alternatively the well may be flooded to a depth sufficient to permit loading or unloading of the platforms solely by floating. The opening between the well and the sea may be permanently open or provided with closure means.
According to another feature of this invention there is provided a special self-elevating vessel for use in carrying out the method of the invention. The vessel comprises: an elongated buoyant hull which is self-propelled, a plurality of jack-up legs removably carried in jacking devices mounted on the vessel, the vessel having a deck providing space for storing the legs in a generally horizontal position; a well in the hull for receiving and discharging a plurality of buoyant platforms through an opening which can be placed in communication with the surrounding water, and a crane mounted on the vessel for movement longitudinally of the vessel, the crane being operable to remove and replace the jack-up legs with respect to their jacking devices and being operable to transport cargo between a ship located on one side of the vessel and a pier structure on the other side of the vessel.